The Effects of Enriched Carbon Dioxide Atmospheres on Plant—Insect Herbivore Interactions

Abstract

Little is known about the effects of enriched CO₂ atmospheres, which may exist in the next century, on natural plant—insect herbivore interactions. Larvae of a specialist insect herbivore, Junonia coenia (Lepidoptera: Nymphalidae), were reared on one of its host plants, Plantago lanceolata (Plantaginaceae), grown in either current low (350 parts per million) or high (700 ppm) CO₂ environments. Those larvae raised on high-CO₂ foliage grew more slowly and experienced greater mortality, especially in early instars, than those raised on low-CO₂ foliage. Poor larval performance on high-CO₂ foliage was probably due to the reduced foliar water and nitrogen concentrations of those plants and not to changes in the concentration of the defensive compounds, iridoid glycosides. Adult pupal weight and female fecundity were not affected by the CO₂ environment of the host plant. These results indicate that interactions between plants and herbivorous insects will be modified under the predicted CO₂ conditions of the 21st century.